1. Field of the Invention
The present invention relates to a scalability used in video coding techniques, and in particular to a spatio-temporal hybrid scalable video coding apparatus using subband decomposition and a method which are capable of improving a coding efficiency and reducing a computational complexity significantly by mixing temporal scalability with spatial scalability.
2. Description of the Prior Art
Generally, in a video communication on the Internet, because a network service quality about a transmission band is not guaranteed, it is difficult to transmit a service such as a moving picture with a high quality stably. In addition, in a decoder having a low processing capacity, it is a frequent occurrence not perfectly decoding received coding data.
Accordingly, in order to provide a service appropriate to a network condition and a decoder's processing capacity, an encoder generates bit stream having a high resolution or a low resolution, and transmits them to a decoder side. When a network condition is deteriorated, although a picture quality is lowered a little, a minimum low resolution quality has to be guaranteed. For that, a scalability method is used.
Scalability means a mechanism, providing various picture qualities in terms of spatial resolution, temporal resolution, and video quality
The scalability can be largely divided into a spatial scalability, a temporal scalability and a SNR (signal to noise ratio) scalability.
The spatial scalability is divided into a EL (base layer) having a low spatial resolution and an EL (enhancement layer) having a high spatial resolution. In the EL, by generating a twice magnified picture in the width and length, namely, a four times magnified picture with respect to a picture of the BL by up-sampling the picture of the BL using an interpolation method, high efficiency encoding can be performed.
In addition, in the temporal scalability in which a frame frequency per one second can be varied while a spatial resolution is constantly maintained, coding is performed by decomposing layers into a BL having a low temporal resolution and can EL having a high temporal resolution. Herein, a picture sequence having a high temporal resolution can be gotten by inserting a B picture into a picture sequence having a low temporal resolution, and a predictive encoding method about a B picture has five modes such as a forward, a backward, a bidirectional, a direct and an intra.
In the meantime, the SNR scalability divides layers into a BL having a low picture quality and an EL having a high picture quality.
However, in the spatial scalability, as described above, the interpolation method is used for up-sampling, in that case, there is no much difference between the total bit quantity and a sum of each bit quantity calculated by each BL and EL. In other words, there is no encoding efficiency improvement as one of advantageousness of scalability.
In addition, when there is one decoder whose capacity includes temporal scalability and spatial scalability, it is required for the decoder to construct separately a temporal scalability processing module and a spatial scalability processing module. Accordingly, a complexity of the decoder is increased.